The field of the invention is, in general terms, that of motor vehicle headlamps. In this field, the headlamps can fulfil various signalling and/or lighting functions, for example side lights, dipped lights, main beam or daytime lights.
Two types of lighting and/or signalling module are essentially known, each having a distinct structure: traditional optical modules and elliptical optical modules.
Traditional optical modules are composed essentially of a mirror reflector associated with a light source.
An elliptical optical module comprises essentially a light source, a reflector and a convex lens. The light source, the reflector and the lens are disposed so as to produce a light beam of given photometry. For example, for a main beam, the light rays emitted by the light source are approximately horizontal when the elliptical optical module is installed in a motor vehicle.
An intermediate part, referred to as the “intermediary”, and not having any particular optical properties, attaches the convex lens to the reflector.
The elliptical optical module can comprise a shield or cover situated between the reflector and the intermediate part. The shield retains part of the light rays. An elliptical optical module of this type can for example fulfil a dipped light function.
An elliptical optical module without shield on the contrary produces a light beam of relatively high intensity. An elliptical optical module of this type can for example fulfil a main beam function.
The shield may be a fixed shield, that is to say the elliptical module fulfils only one function, or a removable shield, which enables the elliptical optical module to fulfil several functions.
The shield in general terms comprises a supporting flap and an optically active flap.
The optically active flap obstructs at least part of the light rays. The optically active flap comprises an active edge, typically a top edge, defining the cut-off of the light beam. The active edge can be substantially horizontal, in particular in order to fulfil a fog light function, or have another shape according to the current regulations in Europe, the United States and Japan. The optically active flap can have a substantially flat shape, or a slightly curved shape.
In the case of a fixed shield, the support flap and the optically active flap are merged, that is to say the fixed shield comprises only fixed components, in particular a single flap, which serves to obstruct at least part of the light rays emitted by the light source.
In the case of a moving shield, the optically active flap is able to move relative to the support flap. The support flap serves as a support for the optically active flap, which effectively serves to obstruct at least part of the light rays.
The support flap of a moving shield is conventionally substantially flat and conventionally has a U shape. The support flap is fixed to a support piece, generally the reflector itself, so that the plane of the support flap is substantially perpendicular to an optical axis of the elliptical optical module.
The optically active flap can for example pivot about an axis of rotation under the direct or indirect effect of an actuator. The optically active flap can be fixed to a transmission shaft in contact with the actuator. The actuator is controlled by the driver of the motor vehicle. For example, when the driver decides to change from the dipped beam function to the main beam function, the actuator is controlled so that the optically active flap is lowered. The moving shield then does not form an obstacle to the light rays and the beam thus produced has a relatively high intensity.
The actuator is fixed directly to the reflector, or directly to the support flap of the moving shield.
However, the active edge of the optically active flap of the shield, whether it be moving or fixed, may cause optical diffraction. Such diffraction depends directly on the wave-length of the light rays and may give rise to chromatic aberrations.
It is known how to use means of adjusting the chromatics in order to remedy the chromatic aberrations. At least part of the shield may be pushed towards the lens, by virtue of a screw for adjusting the chromatics. The adjustment of the chromatics typically takes place during a setting step prior to the assembly of the elliptical optical module in the motor vehicle.
However, when an elliptical optical module to be shielded is installed in a motor vehicle and the latter is running, the shield may bounce because of external vibrations on the support piece, typically the reflector or the intermediate piece, or on the chromatics adjustment screw where applicable. Such bounces give rise to immediate variations in the light beam produced either in the case of a fixed shield or in the case of a moving shield with an optically active flap raised or in the process of pivoting, and may eventually impair the shield.
The present invention aims to improve the reliability of an elliptical optical module comprising a shield.